In part one
of this article, I wrote about the Hawthorne Audio Silver Iris coaxial
drivers in open baffles. I will now describe my experience of adding
the Silver Iris Augies, 15 inch woofers designed specifically for use
on open baffles.

Hawthorne Audio were quite keen for me to
try the Coaxial drivers on their own to see what they could do. And I
found that on a low baffle, ie with some support for the bass
frequencies from the floor) they performed very well. Indeed, I didn't
think that I needed more bass and was intrigued by what the Augies
could add to the performance. It may seem a drawn-out way of arriving
at the same place, but building these Hawthorne Audio speakers this way
helps in the understanding of what each driver is adding to the
speaker.

For the coaxial driver review, I had done
little more than scrounge some chipboard, cut the apertures, and add
some small wings. I could easily have obtained some more free chipboard
and built larger baffles to accommodate both the coaxial and Augie. But
experience has taught me that we have to be careful with this type of
speaker. The vibrations from the bass drivers (and we are talking large
drivers here) can adversely affect the operation of the driver(s)
handling the higher frequencies. And don't forget that although there
is no 'box' to add sound, a baffle is also capable of making an
unwanted contribution unless we take precautions. So I felt that
something more sophisticated was required for this part of the review
to do full justice to the drivers.

I've been building open baffle speakers
for a few years now and have always liked to experiment. As already
stated, the comparative simplicity of an open baffle means that they
can be built much more quickly than a boxed speaker, and this should
encourage us to try different types of baffle. One of the strangest
designs that I have tried was an all polystyrene type with the drivers
bolted to an MDF 'skeleton'. You can read all about that here.
Although I only used a very cheap driver, the results were very
encouraging, with clarity being one of the most noticeable aspects of
the sound. I put that down to the polystyrene baffles having almost no
mass, and therefore no stored energy, so they couldn't add any sound of
their own. But those were only lightweight 8 inch drivers, and this
time I was looking to support a pair of much heavier 15 inch drivers.

After thinking about the problem for a
while, I came up with the idea of a wooden frame that would support the
polystyrene baffles. The frame itself would be lightweight and the
polystyrene would isolate it from the drivers. The next consideration
was how to mount the drivers. You obviously can't bolt or screw
anything to polystyrene so fixing the driver rim to the baffle is not
possible. But I had already become interested in alternative ways of
mounting drivers and read reports of people securing the driver by the
magnet. That seemed like the way to go but I soon realised that drawing
a suitable design on paper was one thing; actually building it was
another. So it was back to the drawing board. Then I had the idea of
mounting the driver by clamping the basket instead of the magnet. This
would entail making some hooks to 'grab' the basket frame. And if the
hooks were threaded, they could be secured with nuts that when
tightened would pull the driver back into the polystyrene baffles,
holding them securely in place.

In fact, this design turned out to be relatively simple to achieve and
seems to work very well. The front of the driver (the rim) is held
securely in a rebate in the polystyrene. Rebating the polystyrene with
a router was very easy but I looked liked a snowman afterwards! (Never
try this indoors unless you live on your own) By tensioning the
securing bolts, the drivers are pulled into the rebates and held
firmly. Only two 'hook-bolts' are required per driver making it quite a
fast job to install or remove them. Each driver sits in its own piece
of two inch (5 cm) thick polystyrene just to isolate them from each
other a bit more. This may be overkill but it wasn't very much more
work to do so I went for it as it also allowed a brace across the
middle of the frame to increase rigidity. And that's about it. Six
pieces of timber for the frame, two upright posts at the rear to bolt
the drivers to, top and bottom decor pieces, and some polystyrene. The
front of the baffle was covered in some thick carpet underlay-felt and
then some thin black felt was wrapped right around the baffle. The
grille cloth is then attached to two batons and stretched around the
whole baffle. Some rear grilles would finish the job nicely! For the
amount of work required, and the cost of materials, I think you will
agree that it looks quite classy (a bit like a Quad ESL63?). Although I
was only reviewing the drivers, I felt obliged to present the product
as well as possible (and uphold the high standard of TNT reviews).

Before we get on to how it all sounds, I
had better tell you about what I used to drive the new baffles.
Hawthorne Audio call their baffles with the two drivers 'Duets', so
that's what I'll call the review baffles for the rest of this review.

As stated in part one, the SI coaxial
drivers come with the their own crossover. However, the Augies require
that some sort of crossover by used to roll them off, either the
passive type (an inductor between power amp and driver), or the active
type, (used between pre amp and power amp). I am much more of a fan of
active crossovers and fortunately, my own open baffle set-up uses an
active crossover for the bass woofers that has a variable setting for
the crossover point. As I also had the four channel Audiodigit CT
MC4x100 amplifier 'on review', it seemed sensible to use that too.

I thought that it may be a good idea to see how the coaxials sounded on
their own in the new baffles so I didn't connect up the Augies. The
coaxials did sound quite different on the higher baffles and this
brings me to an important point. Changing the shape, size and
construction methods of an open baffle speaker nearly always changes
the sound in some way. That's the reason you will often hear the advice
to experiment when you build this type of speaker. With the coaxial
drivers further off the floor, the sound went back to sounding a bit on
the thin side. In addition to that, the baffle was clearly adding less
sound than the simple panel of chipboard that I had used previously.

Turning on the signal to the Augies, I
immediately noticed that the 'thin' sound disappeared. I played around
with the active crossover, settling on a cut-off point of around 55 hz.
At first I had the level control for the active crossover turned nearly
to maximum but as I played more and more music, I found myself reducing
the level quite a bit. I find for this type of job, using my ears and
playing a wide variety of material is the best way to get everything
set up optimally.

When I was happy that I had got the
settings more or less spot on, I sat down to listen. And straight away,
I could see the advantage of using the two drivers together. With the
coaxials raised further off the ground, they seem to gain a little more
clarity. Perhaps this is because they are not producing so much bass.
Anyway, with the Augies 'helping' with the lower frequencies, there is
still that very tuneful, solid, bottom end. Even more so than with the
Coaxials on their own, the Duets, produce wonderful bass even at low
volume settings.
I have found myself listening to CD's that I had
previously reserved for day-time listening, when I could play them
louder without worrying about the neighbours. With the Duets, I can
play them late at night, still enjoying the bass lines, and not
worrying about upsetting anybody else.

I'm not sure if it is connected with
adding the Augies, or some other factor, but listening to the Duets, I
didn't get that impression of the slightly rising response (that I had
noticed using the coaxials on their own). No longer did I feel the need
for a bit of a notch filter on the Behringer DEQ2496! The Duets are
wonderfully 'even-handed' right across the frequency range. Even
playing loud, there is nothing 'offensive'.
I'm not sure exactly how
low they go, I don't have accurate enough equipment to measure them but
I did do a room correction on the DEQ2496 and apart from the usual room
suck outs, the DEQ2496 didn't need to boost any frequency down to 30
hz. (Please note, all the comments about the Duets are made after
listening without the DEQ2496 and in fact, I prefer the sound
without the room correction). The impression that you get with the bass
is that it is lower than it actually is. And of course, being dipole
bass, it's remarkably clear and well defined, and doesn't cause any
room problems, even in my moderately sized sitting room. On 'Sister
drum' by Dadawa, the bass literally 'thunders' but is always
well-controlled.

Timing is also very good. Paul Simon's
'Graceland' had my foot tapping right through the album. If you thought
that large drivers could not produce 'speed' then the Duets will really
enlighten you. It's hard not to get up and dance sometimes!

What you get with the Duets is a 'big'
sound. Sound stage is large and individual performers on a good
recording are life size. When the recordings get complicated, the Duets
just sail on, keeping everything where it should be. When there is a
lot of bass content, that is portrayed clearly without affecting the
clarity of the mid range and higher frequencies.
Percussion is
brilliant, with the passive crossover showing no signs of dulling the
dynamics or transients. Vocals are clear and natural. Everything I have
played through the Duets sounds great; this is not one of those
speakers that excels at say jazz but not rock. It compels you to
rediscover your (whole) music collection.

Perhaps the only thing I can 'criticise'
the Duets on, is that vocals are not quite as good as with my Goodmans
201s. But it's worth repeating, the 201's run without a crossover and
don't have quite as wide a frequency range as the Silver Iris coaxials.
If I am totally honest, the mid-range aside, the Duets better my own
open baffles over-all, and take up less space!

Before I conclude a review, I usually ask myself if I have covered everything,
particularly the negative points. This time, I honestly can't think of
anything negative to say other than this type of speaker may be
physically too large for some people/rooms. Remember that apart from
the size, an open baffle speaker really likes at least a couple of feet
(60 cm) between it and the adjacent walls. I'm not saying that these
are the best speakers in the world, they are not but they are much
nearer the top end than the bottom!
For their cost, and the relatively
small amount of work to build them, I can't think of anything at (or
near) the same price that can produce the same quality of performance.
At the current price, a set of drivers and the passive crossover are
comparable with what we could consider 'entry-level' kit speakers.
Given that the Duets sound like high-end speakers, I know what I would
spend my money on! And going back to the size issue, when they are
finished in that grille cloth, they almost blend into the room like a
piece of furniture.
They are certainly far less obtrusive than my open
baffle speakers that use smaller drivers! Personally, listening to
them, I wouldn't begrudge them the space even if they didn't look so
good!

Summing up, this is possibly the best way
to DIY open baffle speakers for anybody, regardless of their previous
experience. It's really not that expensive for what you get. You don't
need to design or build a crossover.
Even if you have zero DIY skills,
a local carpenter should be able to make you baffles at a reasonable
price. I'm forwarding full details of my baffle design to Hawthorne
Audio who will make them available as part of their excellent customer
service. (Of course, there may be an even better sounding design)
Hawthorne are a tiny company looking to further the cause of hi-fi as
much as make their fortune.
To that end they really go the full
distance in looking after their customers to the extent that even if
you have no knowledge of building speakers, you needn't worry about
tackling something like the Duets for yourself! If you have been
intrigued by the idea of open baffle speakers but didn't know how to
get started, going the Silver Iris route is as good as any!